The present invention relates to an electromagnetic flowmeter for measuring flow rates in lines for conveying and distributing electrically conducting liquids.
Electromagnetic flowmeters for electrically conducting liquids are known. Said flowmeters generally comprise a rigid tubular body that is lined internally with a layer of electrically insulating material. Said layer accommodates two coils, which are supplied with electric power so as to generate a magnetic field with magnetic induction lines that pass through the tubular body and are orientated substantially at right angles to its axis.
Two electrodes are arranged on the internal surface of the electrically insulating body in two diametrically opposite regions, so that the imaginary line that connects the electrodes is substantially perpendicular to the induction lines of the magnetic field.
The flowmeter is connected, by means of the axial ends of the tubular body, to the two segments of a duct along which the flow-rate is to be measured. According to the requirements, the ends of the tubular body can be flanged, threaded or flattened in order to be interposed between two mating flanges (an embodiment commonly known as wafer).
These flowmeters are provided with a converter, which can be mounted on the tubular body or can be arranged remotely with respect to said body. The converter usually comprises a microprocessor that controls the power supply of the coils for generating the magnetic field and is connected to the pair of electrodes so as to detect the potential difference generated between the electrodes. The microprocessor can be connected to a display, which presents visually the flow-rate, which is correlated to the sensed potential difference, or can be connected to another remote monitoring element that constantly monitors the flow-rate measured by the electromagnetic flowmeter.
The operation of these flowmeters is based on Faraday""s law regarding the induction of an e.m.f. at the ends of a conductor of length l moving at a velocity v within a magnetic field. According to this law, in fact,
e=kxc2x7Bxc2x7lxc2x7v
where B is the magnetic induction produced in the conductor by the magnetic field, e is the e.m.f., and k is a scale constant. In the flowmeter being considered, l is the length of the fluid thread that, in each instant, connects the two electrodes. Since the intensity of the magnetic field, i.e., B, is usually constant, and since the passage section of the tubular body in the sensing region is constant, the flow-rate Q is:
Q=Kxc2x7e
The converter, by detecting the potential difference e between the electrodes and multiplying it by K, automatically provides the value of the flow-rate Q.
These kinds of flowmeter ensure high reliability in operation and excellent precision in the measurement made (on the order of +/xe2x88x920.2% of the sensed value), but have the problem of having high manufacturing costs.
On the other hand, in many fields that can accept less precise measurements, such as for example in water distribution, the need is felt to have flowmeters that have low purchase and installation costs.
The aim of the present invention is to provide an electromagnetic flowmeter for measuring flow rates in lines for conveying and distributing electrically conducting liquids, which can be manufactured and installed with considerably lower costs than those entailed by conventional types of electromagnetic flowmeter.
Within this aim, an object of the invention is to provide a flowmeter that despite having a reduced production cost nonetheless ensures a measurement precision that is capable of fully meeting the requirements of various fields of application.
This aim and these and other objects that will become better apparent hereinafter are achieved by an electromagnetic flowmeter for measuring flow rates in lines for conveying and distributing electrically conducting liquids, comprising a flowmeter body that forms a substantially cylindrical chamber, which is delimited by side walls made of electrically insulating material and is open at its ends; said flowmeter body accommodating a pair of mutually facing electrodes arranged in two diametrically opposite regions of the lateral surface of said chamber and means for generating a magnetic field with induction lines that are orientated substantially at right angles to the line that connects said pair of electrodes and to the axis of said chamber; said pair of electrodes being connectable to means for measuring the potential difference induced between said electrodes by the flow of an electrically conducting liquid through said chamber in the presence of said magnetic field, characterized in that said flowmeter body has two sleeves that extend said chamber at its ends, said sleeves being flexible and suitable to be fitted hermetically over the two duct portions along which the flow-rate is to be measured.